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foci    
focus的复数形

focus的复数形

Focus \Fo"cus\ (f[=o]"k[u^]s), n.; pl. E. {Focuses}
(f[=o]"k[u^]s*[e^]z), L. {Foci} (f[=o]"s[imac]). [L. focus
hearth, fireplace; perh. akin to E. bake. Cf. {Curfew},
{Fuel}, {Fusil} the firearm.]
1. (Opt.) A point in which the rays of light meet, after
being reflected or refracted, and at which the image is
formed; as, the focus of a lens or mirror.
[1913 Webster]

2. (Geom.) A point so related to a conic section and certain
straight line called the directrix that the ratio of the
distance between any point of the curve and the focus to
the distance of the same point from the directrix is
constant.
[1913 Webster]

Note: Thus, in the ellipse FGHKLM, A is the focus and CD the
directrix, when the ratios FA:FE, GA:GD, MA:MC, etc.,
are all equal. So in the hyperbola, A is the focus and
CD the directrix when the ratio HA:HK is constant for
all points of the curve; and in the parabola, A is the
focus and CD the directrix when the ratio BA:BC is
constant. In the ellipse this ratio is less than unity,
in the parabola equal to unity, and in the hyperbola
greater than unity. The ellipse and hyperbola have each
two foci, and two corresponding directrixes, and the
parabola has one focus and one directrix. In the
ellipse the sum of the two lines from any point of the
curve to the two foci is constant; that is: AG GB =
AH HB; and in the hyperbola the difference of the
corresponding lines is constant. The diameter which
passes through the foci of the ellipse is the major
axis. The diameter which being produced passes through
the foci of the hyperbola is the transverse axis. The
middle point of the major or the transverse axis is the
center of the curve. Certain other curves, as the
lemniscate and the Cartesian ovals, have points called
foci, possessing properties similar to those of the
foci of conic sections. In an ellipse, rays of light
coming from one focus, and reflected from the curve,
proceed in lines directed toward the other; in an
hyperbola, in lines directed from the other; in a
parabola, rays from the focus, after reflection at the
curve, proceed in lines parallel to the axis. Thus rays
from A in the ellipse are reflected to B; rays from A
in the hyperbola are reflected toward L and M away from
B.
[1913 Webster]

3. A central point; a point of concentration.
[1913 Webster]

{Aplanatic focus}. (Opt.) See under {Aplanatic}.

{Conjugate focus} (Opt.), the focus for rays which have a
sensible divergence, as from a near object; -- so called
because the positions of the object and its image are
interchangeable.

{Focus tube} (Phys.), a vacuum tube for R[oe]ntgen rays in
which the cathode rays are focused upon the anticathode,
for intensifying the effect.

{Principal focus}, or {Solar focus} (Opt.), the focus for
parallel rays.
[1913 Webster]


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  • FOCI Definition Meaning - Merriam-Webster
    The meaning of FOCUS is a center of activity, attraction, or attention How to use focus in a sentence Did you know?
  • Foci - definition of foci by The Free Dictionary
    Define foci foci synonyms, foci pronunciation, foci translation, English dictionary definition of foci n A plural of focus American Heritage® Dictionary of the English Language, Fifth Edition
  • What are Foci in the Brain? – Radiology In Plain English
    Clinical Significance of Brain Foci Brain foci have an important impact on clinical practice and patient care: 1 Diagnosis The identification of brain foci plays a pivotal role in diagnosing a wide array of neurological disorders, including brain tumors, strokes, epilepsy, and neurodegenerative diseases 2 Treatment Planning
  • What Does the Medical Term “foci” Mean? - Reference. com
    Foci are cells located in a specific organ of the body that are notably different from the surrounding cells These differences are caused by mutation or other types of cellular damage, and they’re generally the first sign of a developing lesion, tumor or other disease
  • FOCI | definition in the Cambridge English Dictionary
    Foci left the center of the nucleus and relocated near the envelope membrane, then decondensed; the nuclear membrane folded on itself
  • Foci | definition of foci by Medical dictionary
    foci Plural of focus While this is generally pronounced in the UK as it is in the US, there exists a less common UK-specific pronunciation, which is usually used at an academic level
  • FOCI Definition Meaning | Dictionary. com
    The fasting mice had better blood values, less fatty liver and liver inflammation and above all: they developed less liver cancer and had fewer cancer foci in the liver
  • FOCI | English meaning - Cambridge Dictionary
    For example, a column in a facade and a column in structural analysis would have different meanings, and should therefore have different representational foci
  • Foreign Ownership, Control or Influence
    A company's FOCI factors are reviewed as part of the facility clearance process and throughout the life of the facility security clearance The company's FOCI factors should be documented on the Certificate Pertaining to Foreign Interests (Standard Form 328)





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